Now, I'm waiting on VIZ to get back to me with some comment, but in the meantime, let's go through some of the reactions.
The Comics Reporter and others find it odd that the female-focused magazine would shift readers to Shonen Jump, but it actually makes more sense than it might seem to on the surface. First off, female readers in Japan and North America as a whole tend to follow shounen series as often as shoujo series (much more than male readers follow shoujo). The most popular mangabon in Japan with women is Shounen Jump, after all. And it makes a lot of sense as a business decision: in addition to shedding whatever weight Shojo Beat was carrying, Shonen Jump gets a sudden boost in subscriber numbers, which could potentially boost the selling price of ads in the mag.
The Honolulu Star-Bulletin's Jason Yadao suggests that the reason for Shojo Beat's lesser popularity is that VIZ's “big three” in shoujo are Vampire Knight, Nana, and Ouran High School Host Club, of which only Vampire Knight has been running in the magazine. By contrast, Shonen Jump has Naruto, One Piece, and Bleach still running. Of course, the fact of the matter is that even VIZ's “big three” in shoujo aren't anywhere near as big as Shonen Jump's, and looking at the rest of the manga line, there aren't a lot of obvious best-selling titles. Popular titles, sure, like Honey & Clover, Love*Com, S*A, Skip Beat!, and others, but none that we're seeing a lot of on the sales charts.
Kuri-Ousity, who has done a fair bit of the detective work here, finds that some retailers are still listing an August Shojo Beat, which contrasts with word from the magazine servicing company Alini. Probably safer to bet on the July issue being last, however.
We're still without commentary from some of the leading manga experts, which I'm sure will be appearing within the next day or two. Stay tuned here for more, including (I hope!) some official word from VIZ.
Sources: ANN, The Comics Reporter, Kuriousity, JSYadao@Twitter